After the enterprise follows the borg sphere into the past, its made known that the shields are down. However a few moments later, when Worf fires at the sphere, you can see flashes of the shields. Very strange if you ask me.

Come on people this isn't rocket science, When Worf says "The Shields are down" He's talking about the Enterprise's Shields. At no time was the Borg's Shields mentioned. Later in the Film Picard says: "OUR SHIELDS were down, their vessel was doomed, they'll assimilate the Enterprise and then.....Earth"

The light was made by the torpedos being fired, and detonating. The Borg cannot adapt to meteorites, asteroids or anything like that. They can only adapt to ENERGY signatures. This explains why Picard was able to kill the Borg in the holodeck with the tommy-gun. IF the Borg could adapt to stuff like that, it would've been maybe two shots before the bullets became ineffective, Picard was assimilated, and first contact with the Vulcans was halted.

Just out of curiosity, I wonder why the crew didn't replicate ballistic weapons and kill the Borg due to the fact the Borg cant adapt. If the holodeck can produce the weapon the replicator should be able to manufacture one.

I have no doubt that the borg can adapt to asteroids/bullets/anything without an energy signature, but in episodes/movies where they do adapt, it takes a few second for this to happen..Not quick enough when in a hail of bullets. Apart from which, would a holographic bullet not have an energy signature?

Navigational sheilds for Federation vessels, as someone said, are used to deflect space dust and small asteroids. At warp speeds, even a small rock could do some serious damage to a ship, just like a small bullet going 1000 feet per second does some serious damage to the human body. Check the library at Startrek.com if you don't believe me. Navigational sheilds DO exist.

Well, for one, navigational shields are there to ward off micrometeorites and other small galactic debris, not full-scale phaser blasts. The navigational shields wouldn't have even held out past the first picosecond (millionth), much less a full blast. Two, Borg don't need navigational shields. If they can adapt to a quantum torpedo, then they can certainly adapt to some asteroids. So this is definitely a flub. But you tried to defend it, and that's what counts.